When did we fall for the idea of paying extra for the privilege of being able to buy something? Anyone who handles utility bills knows that there's often a discount for paying by direct debit, but some companies – BT included – actually charge customers extra if they continue to pay in the old-fashioned way. So it is with theatre tickets. Buy a ticket through an agency and you're likely to be charged a hefty booking fee. A report by Which? almost 18 months ago criticised the high charges imposed by many agencies, who in some cases add up to 30% to the face value of a ticket. During the summer a friend of mine paid £67.50 for a ticket for La Cage Aux Folles. The face value was £54, something which was not apparent to her until she arrived at the theatre and collected the ticket.

Some customers will use agencies for the sake of convenience (although much of my own experience with ticket agencies has been seriously stressful). But if you're booking directly with a theatre, then surely you shouldn't pay a booking fee? Think again. Book through the Ambassadors group for a show at one of their venues and you will find yourself coughing up between £2.75 and £4 for the privilege. And it's not just West End theatres that are playing this game. If you want to see a show at the Barbican, they will charge you £2.50 to book by telephone; £1.50 to do it online. Thanks for that. Curiously the Lyceum in Edinburgh has no booking fee if you telephone, but charges £1 per ticket for online bookings, while the Exchange in Manchester charges £2 for online bookings – both of which you would have thought would be less time-consuming for staff to process. The National Theatre and the Royal Shakespeare Company are exemplary in having no booking fees, but many regional theatres charge you to buy a ticket.

Most theatres are quite upfront about their charges, but others are rather less transparent. If you ring the Lyric Hammersmith, for example, a message tells you that it doesn't charge a booking fee, but its box office is on a premium-rate telephone number where the revenue is shared between the telephone company and the theatre; you'd have to look online to discover that it could be costing you up to 10p a minute from a landline. This can add up, particularly when you have to sit through a message that rather disingenuously tells you that they won't be charging a booking fee because they are a charity, and then asks you to make a £1 donation to their work with young people. No one would deny that the Lyric's work with young people is utterly terrific, but should any theatre be using an 0871 number to raise revenue?

Even more insidious is the way that booking numbers directing you to agencies are being editorialised. The La Cage ticket booked by my friend was bought after looking through Time Out and ringing the number in the listings. She thought that she was ringing the theatre, but in fact it was a ticket agency who shared revenue for every ticket bought with Time Out. (The agency in question – the one that added £13.50 to the the ticket – has since been replaced by another, which assured me that it never adds more than a 10% booking fee to any transaction.)

But perhaps we have only ourselves to blame. Until recently the 50-seat Finborough theatre, which doesn't have the resources to accept credit card bookings on its own, operated an old-fashioned telephone-booking system that allowed people to phone in advance and reserve tickets, then turn up on the night to pay and collect. For years this had worked well. But increasingly they discovered that people just didn't bother to show up, or would book six tickets in advance only for two people to come. The result was a show that was sold-out well in advance, but ended up playing to a half-empty auditorium. Moving to a ticket agency means that the theatre's box-office income is protected. You certainly can't blame them for wanting to do that.

• This blogpost was amended on 29 October 2009. The original said thatbooking fees at Sheffield theatres were rising from 50p to £2.75. Thisreference has been removed. (They are rising to 75p.)